1. Field of the Invention
The invention relates to control that enables an exhaust gas control catalyst to effectively demonstrate the ability to purify exhaust gas in an internal combustion engine having a plurality of cylinder groups.
2. Description of the Related Art
One known exhaust gas control apparatus has an individual catalyst arranged in the exhaust passage of each cylinder group and another catalyst arranged downstream of the location where the exhaust passages merge together in an internal combustion engine having a plurality of cylinders sets, such as a so-called V-type internal combustion engine. Both Japanese Patent Application Publication No. 8-121153 (JP-A-8-121153) and Japanese Patent Publication No. 1-27246 (JP-B2-1-27246) describe examples of this kind of exhaust gas control apparatus.
In this kind of exhaust gas control apparatus, the oxygen storage capacity (hereinafter simply also referred to as “OSC”) of each catalyst changes depending on the operating state of the internal combustion engine. Accordingly, unless the OSC of each catalyst is appropriately controlled, the ability of each catalyst to purify exhaust gas is not able to be utilized effectively.